1. Field of the Invention
The present invention relates to a cleaning blade removing a toner remaining on a photoreceptor after a toner image is transferred onto a transfer paper or an intermediate transferer in an image forming apparatus, and to an image forming apparatus and a process cartridge using the cleaning blade.
2. Description of the Related Art
Conventionally, in an electrophotographic image forming apparatus, an unnecessary residual toner adhering to the surface of an image bearer such as photoreceptors to be cleaned after a toner image transferred onto a transfer paper or an intermediate transferer is removed by a cleaner as a cleaning means.
As a cleaning member of the cleaner, a reed-shaped cleaning blade is known because of having a simple structure and good cleanability. The cleaning blade is formed of a reed-shaped elastic body such as polyurethane rubbers. The base of the cleaning blade is supported by a supporting member and the edge thereof is pressed to the circumferential surface of an image bearer to dam and scrape a toner remaining thereon.
Further, an almost spherical polymerization toner having a small particle diameter has been used in image forming apparatuses recently to produce high quality images. The polymerization toner has higher transferability than conventional pulverization toners. However, the polymerization toner is difficult to fully remove from the surface of the image bearer, resulting in poor cleaning. This is because the spherical polymerization toner having a small particle diameter scrapes from the narrowest gap between the blade and the image bearer.
A contact pressure between the image bearer and the cleaning blade needs increasing to prevent the toner from scraping from the gap. However, when the contact pressure is increased, a friction between an image bearer 3 and a cleaning blade 62 in FIG. 8A increases, the cleaning blade 62 is drawn in a travel direction of the image bearer, and an edge 62c of the cleaning blade 62 turns over. The cleaning blade 62 turned over occasionally makes noises when restored to its original state, resisting turning over. Further, when the cleaning continues while the edge 62c of the cleaning blade 62 is turned over, a local abrasion is made a few μm from the edge 62c of an proximal face 62a of the cleaning blade 62 as shown in FIG. 8B. When the cleaning continues further, the local abrasion becomes large and finally the edge 62c is chipped as shown in FIG. 8C. When the edge 62c lacks, a toner cannot normally be removed, resulting in poor cleaning.
Japanese Patent No. 3602898 discloses a cleaning blade formed of polyurethane elastomer including a surface layer formed of a resin having a hardness of pencil hardness of from B to 6H, which contacts a photoreceptor. The surface layer having a hardness of pencil hardness of from B to 6H, which is harder than a rubber member, can decrease a friction coefficient of a contact point of the cleaning blade and increase the abrasion resistance thereof. In addition, a frictional force between the image bearer and the cleaning blade can be reduced, and which can well prevent the edge of the cleaning blade from turning over. Further, the surface layer having a hardness of pencil hardness of from B to 6H is hard and difficult to deform, and which can furthermore prevent the edge of the cleaning blade from turning over.
Japanese published unexamined application No. 2004-233818 discloses a cleaning blade, on the surface of which a hardened layer is formed by impregnating and swelling an elastic blade with a silicon-containing UV curable material, and irradiating the blade with an UV ray. The hardened layer formed of the UV curable material improves the abrasion resistance of the elastic blade and can prevent the edge of the cleaning blade from turning over.
However, the cleaning blade having a (hardened) surface layer occasionally has poor cleanability. The present inventors found that the edge needs to make a stick and slip movement such that the cleaning blade has goof cleanability. The stick and slip movement means that the edge elastically deforms in a travel direction of a photoreceptor due to friction therewith and the edge restores the original form slipping on the surface thereof at a point where the blade has a restoring force larger than the friction. Then, the edge elastically deforms again in a travel direction of a photoreceptor due to friction therewith. This reciprocating movement is the stick and slip movement. When a friction coefficient between the (hardened) surface layer and the photoreceptor is too low, the friction therebetween is so small that the edge does not make the stick and slip movement and more toners scrape through between them. When the friction coefficient between the (hardened) surface layer and the photoreceptor is high, the edge fully makes the stick and slip movement and the blade has good cleanability. However, when the friction coefficient between the (hardened) surface layer and the photoreceptor is high, an oscillation noise is made.
Because of these reasons, a need exists for a cleaning blade having good cleanability, preventing its edge from turning over and making an oscillation noise.